Provided are a method and device for transmitting MSG3 in a random access procedure in a wireless communication system. A user equipment (UE) determines a frequency resource for transmitting MSG3 in a random access procedure and transmits the MSG3 to a network via the frequency resource. The starting position of the frequency resource is the smallest physical resource block (PRB) of an active uplink (UL) bandwidth part (BWP), and the bandwidth of the frequency resource is the same as the bandwidth of an initial UL BWP.